Pipe Element Having Wedging Groove

ABSTRACT

A pipe element has a circumferential groove with a surface portion oriented at an angle with respect to its longitudinal axis. A surface portion of the groove adjacent to the angled surface portion is oriented perpendicular to the longitudinal axis. A mechanical coupling has projecting keys that engage the groove. The keys have mating surfaces that contact both the perpendicular and angled surface portions of the groove. When the pipe element and coupling are used in combination to form a pipe joint, axial load on the pipe, resisted by the mechanical coupling, is shared between the perpendicular and angled surface portions which results in a pipe joint that can withstand higher internal pressure than if the axial load were borne by the perpendicular surface portion alone.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Pat. Application No.16/693,973, filed Nov. 25, 2019, which application is a continuation ofU.S. Pat. Application No. 15/409,688, filed Jan. 19, 2017, whichapplication is based upon and claims priority to U.S. ProvisionalApplication No. 62/287,015, filed Jan. 26, 2016, all applications beinghereby incorporated by reference.

FIELD OF THE INVENTION

This invention concerns improved groove shapes for pipe elements joinedby mechanical couplings, and coupling key shapes compatible withimproved groove shapes.

BACKGROUND

As shown in FIG. 1 , one type of prior art mechanical coupling 10 forjoining pipe elements 12 and 14 end to end relies on arcuateprojections, known as keys 16 that mechanically engage circumferentialgrooves 18 in the pipe elements. While these couplings have proved to bevery effective and efficient, the prior art configuration is subject tocertain limitations. For example, when such a joint is subjected toloads, especially loads arising from internal pressure induced endloads, axial tensile forces and bending, the joint may not be able towithstand such loads up to the full tensile strength of certain types ofpipe. To realize a greater percentage of the potential strength of thepipe element and thereby increase the pressure capacity of a joint,external rings containing grooves may be welded to pipe elements toprovide for mechanical engagement with the coupling’s keys in aconfiguration that does not alter the pipe element’s sidewall, either byremoving material (machined grooves) or by deforming the sidewall(rolled grooves).

While welded external rings may permit a larger percentage of the fullpipe strength to be realized at a joint, the disadvantage of thissolution is the need to weld rings onto the pipe elements. Thisprocedure adds cost, time and requires skilled welders, complicatingfabrication. There is clearly a need for a pipe design that improves therealization of pipe element strength and thereby increases the internalpressure performance and axial tensile loading limits achievable usingmechanical couplings without the need for external welded rings.

SUMMARY

The invention concerns a pipe element having first and second oppositelydisposed ends. In one example embodiment the pipe element comprises asidewall surrounding a longitudinal axis and defining a bore. Thesidewall has an outer surface. A first groove is positioned in the outersurface. The first groove extends circumferentially around the bore andis positioned proximate to the first end. The first groove is defined bya first plurality of sub-surfaces of the outer surface including:

-   a first sub-surface oriented at an angle with respect to the    longitudinal axis and facing away from the first end;-   a second sub-surface oriented at an angle with respect to the    longitudinal axis, the second sub-surface being in spaced relation    away from and facing toward the first sub-surface;-   a third sub-surface contiguous with the first sub-surface, the third    sub-surface oriented at an angle with respect to the longitudinal    axis and sloping toward the second sub-surface; and-   a fourth sub-surface contiguous with the third and second sub    surfaces, the fourth sub-surface being oriented at an angle with    respect to to the longitudinal axis.

In a specific example embodiment the first sub-surface has anorientation angle from 80° to 90° with respect to the longitudinal axis.Further by way of example, the first sub-surface has an orientationangle of 89° with respect to the longitudinal axis. In another example,the third sub-surface has an orientation angle from 1° to 25° withrespect to the longitudinal axis. In a further example, the thirdsub-surface has an orientation angle of 10° with respect to thelongitudinal axis. In another example the second sub-surface has anorientation angle of 90° with respect to the longitudinal axis. Furtherby way of example, the second sub-surface has an orientation angle from40° to 70° with respect to the longitudinal axis. In an exampleembodiment the second sub-surface has an orientation angle of 50° withrespect to the longitudinal axis. In a further example embodiment thefourth sub-surface has an orientation angle from +5° to -5° with respectto the longitudinal axis.

In an example embodiment the pipe element further comprises a secondgroove positioned in the outer surface. The second groove extendscircumferentially around the bore and positioned proximate to the secondend. The second groove is defined by a second plurality of sub-surfacesof the outer surface including:

-   a fifth sub-surface oriented at an angle with respect to the    longitudinal axis and facing away from the second end;-   a sixth sub-surface oriented at an angle with respect to the    longitudinal axis, the sixth sub-surface being in spaced relation    away from and facing toward the fifth sub-surface;-   a seventh sub-surface contiguous with the fifth sub-surface, the    seventh sub-surface oriented at an angle with respect to the    longitudinal axis and sloping toward the sixth sub-surface; and-   an eighth sub-surface contiguous with the seventh and sixth sub    surfaces, the eighth sub-surface oriented at an angle with respect    to the longitudinal axis.

In another example embodiment the first and fifth sub-surfaces have anorientation angle from 80° to 90° with respect to the longitudinal axis.Further by way of example, the first and fifth sub-surfaces have anorientation angle 89° with respect to the longitudinal axis. In anotherexample, the third and seventh sub-surfaces have an orientation anglefrom 1° to 25° with respect to the longitudinal axis. By way of furtherexample, the third and seventh sub-surfaces have an orientation angle of10° with respect to the longitudinal axis. In another example, thesecond and sixth sub-surfaces have an orientation angle of 90° withrespect to the longitudinal axis. In another example, the second andsixth sub-surfaces have an orientation angle from 40° to 70° withrespect to the longitudinal axis. Further by way of example, the secondand sixth sub-surfaces have an orientation angle of 50° with respect tothe longitudinal axis. In another example, the fourth and eighthsub-surfaces have an orientation angle from +5° to -5° with respect tothe longitudinal axis.

The invention further encompasses, in combination, a pipe element asdescribed above and a coupling. In one example embodiment the couplingcomprises a plurality of segments attached to one another end to endsurrounding the first end of the pipe element. Adjustable attachmentmembers are positioned at each end of the segments for attaching thesegments to one another. At least one arcuate projection is positionedon one side of each of the segments and engages with the first groove.The at least one arcuate projection comprises a plurality of matingsurfaces including:

-   a first mating surface oriented at an angle with respect to the    longitudinal axis and in facing relation with the first sub-surface;-   a second mating surface oriented at an angle with respect to the    longitudinal axis and in facing relation with the second    sub-surface;-   a third mating surface oriented at an angle with respect to the    longitudinal axis and contacting the third sub-surface; and-   a fourth mating surface in facing relation with the fourth    sub-surface.

In an example embodiment a gap is positioned between the fourth matingsurface and the fourth sub-surface. In a further example, the at leastone arcuate projection comprises a recess therein forming the gapbetween fourth mating surface and the fourth sub-surface.

A further example embodiment comprises, in combination, a pipe elementas described above and a coupling. By way of example the couplingcomprises a plurality of segments attached to one another end to endsurrounding the first end of the pipe element. Adjustable attachmentmembers are positioned at each end of the segments for attaching thesegments to one another. At least one arcuate projection is positionedon one side of each of the segments and engages with the first groove.The at least one arcuate projection comprises a plurality of matingsurfaces including:

-   a first mating surface oriented perpendicular to the longitudinal    axis and in facing relation with the first sub-surface;-   a second mating surface oriented perpendicular to the longitudinal    axis and in facing relation with the second sub-surface;-   a third mating surface oriented at an angle with respect to the    longitudinal axis and contacting the third sub-surface; and-   a fourth mating surface in facing relation with the fourth    sub-surface.

By way of example, a gap is positioned between the fourth mating surfaceand the fourth sub-surface. In a further example the at least onearcuate projection comprises a recess therein forming the gap betweenthe fourth mating surface and the fourth sub-surface. In an exampleembodiment the coupling comprises no more than two segments.

The invention also encompasses a coupling for joining pipe elements. Inan example embodiment the coupling comprises a plurality of segmentsattached to one another end to end surrounding a central space forreceiving the pipe elements. Adjustable attachment members arepositioned at each end of the segments for attaching the segments to oneanother. At least a first arcuate projection is positioned on a firstside of each of the segments. The first arcuate projections comprise aplurality of mating surfaces including:

-   a first mating surface oriented at an angle with respect to a    longitudinal axis extending through the central space coaxially with    the segments;-   a second mating surface in spaced relation from the first mating    surface and oriented at an angle with respect to the longitudinal    axis;-   a third mating surface contiguous with the first mating surface and    oriented at an angle with respect to the longitudinal axis; and-   a fourth mating surface between the third and second mating surfaces    and oriented at an angle with respect to the longitudinal axis.

In an example embodiment the pipe element further comprises a secondarcuate projection positioned on a second side of each of the segments.The second arcuate projections comprise a plurality of mating surfacesincluding:

-   a fifth mating surface oriented at an angle with respect to the    longitudinal axis;-   a sixth mating surface in spaced relation from the fifth mating    surface and oriented at an angle with respect to the longitudinal    axis;-   a seventh mating surface contiguous with the fifth mating surface    and oriented at an angle with respect to the longitudinal axis; and-   an eighth mating surface between the sixth and seventh mating    surfaces and oriented at an angle with respect to the longitudinal    axis.

In an example embodiment the first mating surface has an orientationangle from 80° to 90° with respect to the longitudinal axis. In anotherexample embodiment the first mating surface has an orientation angle of89° with respect to the longitudinal axis. By way of further example thethird mating surface has an orientation angle from 1° to 25° relative tothe longitudinal axis. In another example the third mating surface hasan orientation angle of 10° relative to the longitudinal axis. In afurther example the second mating surface has an orientation angle of90° with respect to the longitudinal axis. In another example the secondmating surface has an orientation angle from 40° to 70° relative to thelongitudinal axis. Further by way of example the second mating surfacehas an orientation angle of 50° relative to the longitudinal axis. Inanother example the fourth mating surface has an orientation angle from+5° to -5° with respect to the longitudinal axis. In an exampleembodiment the first and fifth mating surfaces have an orientation anglefrom 80° to 90° with respect to the longitudinal axis. Further by way ofexample, the first and fifth mating surfaces have an orientation angleof 89° with respect to the longitudinal axis. In another example, thethird and seventh mating surfaces have an orientation angle from 1° to25° relative to the longitudinal axis. Further by way of example, thethird and seventh mating surfaces have an orientation angle of 10°relative to the longitudinal axis. Also by way of example, the secondand sixth mating surfaces have an orientation angle of 90° with respectto the longitudinal axis. In an example embodiment, the second and sixthmating surfaces have an orientation angle from 40° to 70° relative tothe longitudinal axis. In a further example, the second and sixth matingsurfaces have an orientation angle of 50° relative to the longitudinalaxis. In another example, the fourth and eighth mating surfaces have anorientation angle from +5° to -5° with respect to the longitudinal axis.

The invention also encompasses, in combination, a coupling as describedabove and a pipe element. In one example embodiment the pipe elementcomprises a sidewall surrounding the longitudinal axis and defining abore. The sidewall has an outer surface. A first groove is positioned inthe outer surface. The first groove extends circumferentially around thebore and is positioned proximate to the first end. The first groove isdefined by a first plurality of sub-surfaces of the outer surfaceincluding:

-   a first sub-surface oriented at an angle with respect to the    longitudinal axis and in facing relation with the first mating    surface;-   a second sub-surface oriented at an angle with respect to the    longitudinal axis and in facing relation with the second mating    surface;-   a third sub-surface oriented at an angle with respect to the    longitudinal axis and contacting the third mating surface; and-   a fourth sub-surface in facing relation with the fourth mating    surface.

In an example embodiment a gap is positioned between the fourth matingsurface and the fourth sub-surface. In an example embodiment the firstarcuate projection comprises a recess therein forming the gap betweenthe fourth mating surface and the fourth sub-surface.

Another example embodiment comprises, in combination, a coupling asdescribed above and a pipe element. By way of example the pipe elementcomprises:

-   a sidewall surrounding the longitudinal axis and defining a bore,    the sidewall having an outer surface;-   a first groove positioned in the outer surface, the first groove    extending circumferentially around the bore and positioned proximate    to the first end, the first groove being defined by a first    plurality of sub-surfaces of the outer surface including:-   a first sub-surface oriented perpendicular to the longitudinal axis    and in facing relation with the first mating surface;-   a second sub-surface oriented perpendicular to the longitudinal axis    and in facing relation with the second mating surface;-   a third sub-surface oriented at an angle with respect to the    longitudinal axis and contacting the third mating surface; and-   a fourth sub-surface in facing relation with the fourth mating    surface.

By way of example a gap is positioned between the fourth mating surfaceand the fourth sub-surface. In an example embodiment the first arcuateprojection comprises a recess therein forming the gap between the fourthmating surface and the fourth sub-surface.

In an example embodiment the coupling comprises no more than twosegments.

The invention also encompasses a method of assembling a coupling havingan arcuate projection with a pipe element. In one example embodiment themethod comprises:

-   contacting the third sub-surface of the groove with a portion of the    arcuate projection;-   contacting the second sub-surface of the groove with another portion    of the arcuate projection.

The invention also encompasses a method of using a coupling having anarcuate projection engaged with a groove of a pipe element. In oneexample the method comprises:

applying a tensile force between the pipe element and the coupling,thereby causing a portion of the arcuate projection to engage the firstsub-surface and another portion of the arcuate projection to engage thethird sub-surface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a pipe joint according to theprior art;

FIG. 2 is an isometric view of an example combination coupling and pipeelements according to the invention;

FIG. 3 is a longitudinal sectional view of a portion of an examplecoupling and pipe elements according to the invention shown initiallyupon assembly;

FIG. 3A is a longitudinal sectional view of a portion of another examplecoupling and pipe elements according to the invention;

FIG. 3B is a longitudinal sectional view of the portion of the examplecoupling and pipe elements shown in FIG. 3 in the fully loadedcondition;

FIG. 4 is a partial longitudinal sectional view of an example pipeelement according to the invention; and

FIG. 5 is a partial longitudinal sectional view illustrating a deviceand a method for forming pipe elements according to the invention.

DETAILED DESCRIPTION

FIG. 2 shows an example mechanical pipe coupling 20 according to theinvention joining example pipe elements 22 and 24 according to theinvention. Coupling 20 comprises segments 26 and 28 attached end to endto surround a central space 30 which receives the pipe elements 22 and24. Attachment of the segments to one another is effected by adjustableattachment members 32 and 34 which, in this example, comprise lugs 36and 38 that respectively project from opposite ends of each segment 26and 28. Lugs 36 and 38 in this example have reinforcing gussets 40 andopenings 42 that receive fasteners 44, in this example studs 46 and nuts48.

As shown in the sectional view of FIG. 3 , each segment (26 being shownin section) has two arcuate projections, also known as keys 50 and 52positioned on opposite sides of each segment. Keys 52 and 50 projecttoward the central space 30 and mechanically engage respectivecircumferential grooves 54 and 88 in each pipe element. A fluid tightjoint is ensured by a ring seal 56 captured and compressed between thesegments 26 and 28 and the pipe elements 22 and 24 when fasteners 44(see FIG. 2 ) are adjustably tightened to draw the segments 26 and 28toward one another and into engagement with the pipe elements to formthe joint.

FIG. 4 shows pipe element 24 and its groove 54 in detail. In thisexample pipe element 24 comprises a sidewall 58 surrounding alongitudinal axis 60 and defining a bore 62. Groove 54 is positioned inan outer surface 64 of the sidewall 58. Groove 54 extendscircumferentially about the bore 62 and is positioned proximate to anend 66 of the pipe element 24. As shown in FIG. 3 , the position of thegroove 54 with respect to the pipe end 66 is coordinated with thecoupling 20 so as to provide lands 70 for sealing engagement with theglands 72 of the ring seal 56.

As shown in FIG. 4 , groove 54 comprises a first sub-surface 74 shownoriented perpendicular (90°) relative to the longitudinal axis 60. Theorientation angle 73 of first sub-surface 74 may range from 80° to 90°with respect to the longitudinal axis 60, with an orientation angle ofabout 89° being advantageous. First sub-surface 74 faces away from theend 66 of the pipe element 24. A second sub-surface 76 is oriented at anangle with respect to the longitudinal axis 60. Second sub-surface 76 ispositioned in spaced relation away from the first sub-surface 74 andfaces the end 66 of the pipe element 24. A third sub-surface 78 iscontiguous with the first sub-surface 74, is oriented at an angle withrespect to the longitudinal axis 60 and slopes toward the secondsub-surface 76. A fourth sub-surface 80 is contiguous with both thesecond and third sub-surfaces. The fourth sub-surface 80 is shownoriented parallel (0° angle) to the longitudinal axis 60, but itsorientation angle 79 may range from +5° to -5° for a practical design.The terms “perpendicular”, “parallel” and “oriented at an angle” meanperpendicular or parallel or oriented at an angle with respect to areference axis within normal manufacturing tolerances for the pipeelement in question.

In a practical design, second sub-surface 76 may have an orientationangle 82 from about 40° to about 70° relative to the longitudinal axis60; an orientation angle 82 of about 50° is considered advantageous forcertain applications. Similarly, the third sub-surface 78 may have anorientation angle 84 from about 1° to about 25° relative to thelongitudinal axis 60, and an orientation angle 84 of about 10° isconsidered advantageous for certain applications.

As further shown in FIG. 4 , pipe element 24 may have a second end 86oppositely disposed from the end 66 (which may thus be considered the“first” end), the second end 86 having a second groove 88 with a grooveconfiguration similar to the first groove 54. In this example embodimentsecond groove 88 comprises a fifth sub-surface 90 shown orientedperpendicular (90°) to the longitudinal axis 60. The orientation angle91 of fifth sub-surface 90 may range from 80° to 90° with respect to thelongitudinal axis 60, with an orientation angle of about 89° beingadvantageous. Fifth sub-surface 90 faces away from the second end 86 ofthe pipe element 24. A sixth sub-surface 92 is oriented at an angle withrespect to the longitudinal axis 60. Sixth sub-surface 92 is positionedin spaced relation away from the fifth sub-surface 90 and faces thesecond end 86 of the pipe element 24. A seventh sub-surface 94 iscontiguous with the fifth sub-surface 90, is oriented at an angle withrespect to the longitudinal axis 60 and slopes toward the sixthsub-surface 92. An eighth sub-surface 96 is contiguous with both thesixth and seventh sub-surfaces. The eighth sub-surface 96 is shownoriented parallel (0° angle) to the longitudinal axis 60, but itsorientation angle 97 may range from about +5° to about -5° for apractical design.

In a practical design, sixth sub-surface 92 may have an orientationangle 98 from about 40° to about 70° relative to the longitudinal axis60; an orientation angle 98 of about 50° is considered advantageous forcertain applications. Similarly, the seventh sub-surface 94 may have anorientation angle 100 from about 1° to about 25° relative to thelongitudinal axis 60, and an orientation angle 100 of about 10° isconsidered advantageous for certain applications.

Grooves 54, 88 may be formed in pipe elements 22 and 24 by rollgrooving, as shown in FIG. 5 . As shown by way of example for groove 54in pipe element 24, the pipe element is cold worked while being rotatedbetween an inner roller 101 that contacts the inside surface 103 of thepipe element, and an outer roller 105 that contacts the pipe elementouter surface 107. Typically, the inner roller 101 is driven (rotatedabout an axis 109 parallel to the longitudinal axis 60 of the pipeelement 24). The driven inner roller 101 rotates the pipe element,which, in turn rotates the outer roller 105 about an axis 111 as aresult of contact friction between the rollers and the pipe element. Theouter roller 105, being an idler, is usually forced toward the innerroller 101 with a hydraulic ram 113, deforming the pipe element andforming the groove 54 having a shape dictated by the shapes of the innerand outer rollers 101 and 105. Grooves 54 and 88 may also be formed bymachining operations.

FIGS. 2 and 3 show a combination pipe element (22 and/or 24) andcoupling 20 connecting the pipe elements end to end. FIG. 3 shows indetail, the cross sectional geometry of the arcuate projections or keys50 and 52 effecting mechanical engagement with circumferential grooves88 and 54 in each pipe element 22 and 24 initially upon assembly of thejoint, i.e. prior to the application of internal pressure induced endloads, axial tensile forces and bending loads.

In this example embodiment, key 52 comprises a plurality of matingsurfaces including a first mating surface 102 shown orientedperpendicular to the longitudinal axis 60 and in facing relation withthe first sub-surface 74. Note initially upon assembly there usuallywill be a gap between first mating surface 102 and first sub-surface 74because the angular relationship between sub-surface 78 and sub-surface80 tends to bias the location of key 52 away from sub-surface 74. Asecond mating surface 104 is oriented at an angle with respect to thelongitudinal axis 60, is spaced away from the first mating surface 102,and contacts the second sub-surface 76 initially upon assembly. A thirdmating surface 106 is oriented at an angle with respect to thelongitudinal axis 60 and is contiguous with the first mating surface102. Third mating surface 106 contacts third sub-surface 78 initiallyupon assembly. A fourth mating surface 108 is between the second andthird mating surfaces 104 and 106, is in facing relation with the fourthsub-surface 80 and in spaced apart relation therefrom thereby forming agap 115. The gap 115 is ensured by the fourth mating surface 108comprising a recess in the arcuate projection (key) 52. Similarly, key50 also comprises a plurality of mating surfaces including a fifthmating surface 110 shown oriented perpendicular to the longitudinal axis60 and in facing relation with the fifth sub-surface 90. A gap istypically present between the fifth mating surface 110 and the fifthsub-surface 90 initially upon assembly because the angular relationshipbetween sub-surface 94 and sub-surface 96 tends to bias the location ofkey 50 away from sub-surface 90. A sixth mating surface 112 is orientedat an angle with respect to the longitudinal axis 60, is spaced awayfrom the fifth mating surface 110, and contacts the sixth sub-surface 92initially upon assembly. A seventh mating surface 114 is oriented at anangle with respect to the longitudinal axis 60 and is contiguous withthe fifth mating surface 110. Seventh mating surface 114 contactsseventh sub-surface 94 initially upon assembly. An eighth mating surface116 is between the sixth and seventh mating surfaces 112 and 114, is infacing relation with the eighth sub-surface 96 and in spaced apartrelation therefrom thereby forming a gap 117. The gap 117 is ensured bythe eighth mating surface 116 comprising a recess in the arcuateprojection (key) 50.

In a practical design, the mating surfaces will have orientation anglesmatched to the respective sub-surfaces they contact. Thus the firstmating surface 102 may have an orientation angle 119 from about 80° toabout 90° with respect to the longitudinal axis 60, with an orientationangle of about 89° being advantageous. The second mating surface 104 mayhave an orientation angle 118 from about 40° to about 70° with respectto the longitudinal axis 60. An orientation angle 118 of about 50° isconsidered advantageous for certain applications. The third matingsurface 106 may have an orientation angle 120 from about 1° to about 25°with respect to the longitudinal axis 60. An orientation angle 120 ofabout 10° is considered advantageous for certain applications. Theorientation angle 121 of the fourth mating surface 108 may range fromabout +5° to about -5° with respect to the longitudinal axis 60.

Similarly, the fifth mating surface 110 may have an orientation angle123 from about 80° to about 90° with respect to the longitudinal axis60, with an orientation angle of about 89° being advantageous. The sixthmating surface 112 may have an orientation angle 122 from about 40° toabout 70° with respect to the longitudinal axis 60. An orientation angle122 of about 50° is considered advantageous for certain applications.The seventh mating surface 114 may have an orientation angle 124 fromabout 1° to about 25° with respect to the longitudinal axis 60. Anorientation angle 124 of about 10° is considered advantageous forcertain applications. The orientation angle 125 of the eighth matingsurface 116 may range from about +5° to about -5° with respect to thelongitudinal axis 60.

FIG. 3A illustrates another example embodiment wherein coupling 20 ajoins pipe elements 22 a and 24 a. In this example embodiment thesub-surface 92 a on pipe element 22 a and its mating surface 112 a onkey 50 a of coupling 20 a are oriented at about 90° to the longitudinalaxis 60. Similarly, sub-surface 76 a on pipe element 24 a and its matingsurface 104 a on key 52 a of coupling 20 a are oriented at about 90° tothe longitudinal axis 60. As evidenced by the absence of gaps betweenmating surface 110 and sub-surface 90 and mating surface 102 andsub-surface 74, the joint is shown subjected to internal pressureinduced end loads and /or axial tensile forces, as explained in detailbelow.

Example pipe elements 22 and 24 (or 22 a and 24 a), when used incombination with the example coupling 20 (or coupling 20 a,respectively) provide a marked improvement over prior art directmechanical roll groove or machined groove coupling systems. The improvedperformance is due to a better axial load distribution, which, unlikeprior art couplings, is not borne entirely at the first and fifthsub-surfaces 74 and 90. Rather, a portion of the axial load is borne bythe sub-surfaces 74 and 90 as a result of contact between the thirdmating surface 106 and the third sub-surface 78 and the seventh matingsurface 114 and the seventh sub-surface 94. These mating surfaces on thecoupling and sub-surfaces on the pipe elements are oriented at an anglewith respect to the longitudinal axis 60. Thus, when, as shown in FIG.3B, the pipe joint is subjected to internal pressure induced end loadsand /or axial tensile forces, the pipe elements 22 and 24 (or 22 a and24 a) move axially away from one another, the aforementioned matingsurfaces 106 and 114 ride up angled sub-surfaces 78 and 94 to come intogreater wedging, clamping contact with the mating surfaces 106 and 114respectively, until mating surfaces 102 and 110 firmly contact the firstand fifth sub-surfaces 74 and 90 of the pipe element 24 and 22 (or 24 aand 22 a). The internal pressure induced end loads and /or axial tensileforces are thus resisted not only by contact between mating surfaces 102and 110 of the coupling and sub-surfaces 74 and 90 of the pipe elements,but also by the wedging, clamping contact of mating surfaces 106 and 114with angled sub-surfaces 78 and 94. Keys 50 and 52 (also 50 a and 52 a)are designed so that they do not completely fill their respectivegrooves 88 and 54. Rather, as the pipe joint is loaded, pipe elements 22and 24 push away from one another until sub-surfaces 74 and 90 come intocontact with mating surfaces 102 and 110 respectively. This will open agap between sub-surfaces 92 and 76 and their respective mating surfaces112 and 114. The spaced relation of the fourth mating surface 108 fromthe fourth sub-surface 80 and the spaced relation of the eighth matingsurface 116 from the eighth sub-surface 96 provide the needed space toensure that contact is achieved between sub-surface 78 and matingsurface 106 as well as between sub-surface 94 and mating surface 114.

The load sharing which provides improved performance is effected by thegeometries of the keys 50 and 52 and the respective grooves 88 ad 54which they engage as well as the method of assembling and using thecoupling and pipe elements according to the invention. In an exampleembodiment of one method of assembly, described for pipe element 24 andcoupling 20 with reference to FIG. 3 , comprises contacting the thirdsub-surface 78 of groove 54 with a portion (third mating surface 106) ofthe arcuate projection (key) 52, and contacting the second sub-surface76 of groove 54 with another portion (second mating surface 104) of thearcuate projection (key) 52. When the combination includes the secondpipe element 22 the assembly proceeds similarly; contacting the seventhsub-surface 94 of groove 88 with a portion (seventh mating surface 114)of the arcuate projection (key) 50, and contacting the sixth sub-surface92 of groove 88 with another portion (sixth mating surface 112) of thearcuate projection (key) 52.

An example method of using the coupling 20 having arcuate projections50, 52 engaged with grooves 88, 54 of the pipe elements 22 and 24 isillustrated with reference to FIGS. 3 and 3B and comprises assemblingcoupling segments 26 and 28 about pipe elements 22 and 24, such thatkeys 50 and 52 are located within grooves 88 and 54, respectively (FIG.3 ). Fasteners 44 are then installed and tightened to connect attachmentmembers 32 and 34 and ensure that at least mating surfaces 106 and 114come into contact with sub-surfaces 78 and 94 respectively. As shown inFIG. 3B, forces are applied to the coupling (arising from systempressure, gravitational or other end loads) which create a tensile forcebetween the pipe elements and the coupling, thereby causing respectiveportions of the arcuate projections (first and fifth mating surfaces102, 110) to engage respective first and fifth sub-surfaces 74 and 90 ofgrooves 54 and 88, and other portions (third and seventh mating surfaces106 and 114) of the arcuate projections 52 and 50 to respectively engagethe third and seventh sub-surfaces 78 and 94.

Pipe elements and their associated couplings according to the inventionhave demonstrated a marked improvement in the goal of realizing agreater portion of the potential strength of the pipe element whencompared to prior art pipe elements and couplings.

What is claimed is:
 1. A method of using a coupling having an arcuateprojection engaged with a groove positioned in an outer surfaceproximate to a first end of a pipe element extending along alongitudinal axis, said groove comprising: a first sub-surface orientedat an angle with respect to said longitudinal axis and facing away fromsaid first end; a second sub-surface oriented at an angle with respectto said longitudinal axis, said second sub-surface being in spacedrelation away from and facing toward said first sub-surface; a thirdsub-surface contiguous with said first sub-surface, said thirdsub-surface oriented at a non-zero angle with respect to saidlongitudinal axis and sloping toward said second sub-surface; and afourth sub-surface contiguous with said third and second sub surfaces,said fourth sub-surface being oriented at an angle with respect to saidlongitudinal axis; said method comprising: contacting said thirdsub-surface with a first portion of said arcuate projection of saidcoupling while maintaining a gap between said first sub-surface and asecond portion of said arcuate projection of said coupling; and applyinga tensile force between said pipe element and said coupling, therebycausing said gap to close and said second portion of said arcuateprojection of said coupling to engage said first sub-surface.
 2. Themethod according to claim 1, wherein said tensile force causes wedgingbetween said third sub-surface and said first portion of said arcuateprojection of said coupling.
 3. The method according to claim 1 furthercomprising: contacting said second sub-surface with a third portion ofsaid arcuate projection of said coupling while maintaining said gapbetween said first sub-surface and said second portion of said arcuateprojection of said coupling.
 4. The method according to claim 3, whereinsaid tensile force causes a second gap to form between said secondsub-surface and said third portion of said arcuate projection of saidcoupling.
 5. The method according to claim 1, wherein said secondsub-surface is oriented at an angle less than 90 degrees with respect tosaid longitudinal axis to bias said arcuate projection of said couplingtowards said third sub-surface and said first sub-surface when saidtensile force is applied.
 6. A method of using a coupling to connect afirst pipe element having a first end and a second pipe element having asecond end, said first and second pipe elements extending along alongitudinal axis, said first pipe element comprising: a first groovepositioned proximate to said first end and configured to receive a firstarcuate projection of said coupling, said first groove comprising: afirst sub-surface oriented at an angle with respect to said longitudinalaxis and facing away from said first end; a second sub-surface orientedat an angle with respect to said longitudinal axis, said secondsub-surface being in spaced relation away from and facing toward saidfirst sub-surface; a third sub-surface contiguous with said firstsub-surface, said third sub-surface oriented at a non-zero angle withrespect to said longitudinal axis and sloping toward said secondsub-surface; and a fourth sub-surface contiguous with said third andsecond sub surfaces, said fourth sub-surface being oriented at an anglewith respect to said longitudinal axis; said second pipe elementcomprising: a second groove positioned proximate to said second end andconfigured to receive a second arcuate projection of said coupling, saidsecond groove comprising: a fifth sub-surface oriented at an angle withrespect to said longitudinal axis and facing away from said second end;a sixth sub-surface oriented at an angle with respect to saidlongitudinal axis, said sixth sub-surface being in spaced relation awayfrom and facing toward said fifth sub-surface; a seventh sub-surfacecontiguous with said fifth sub-surface, said seventh sub-surfaceoriented at a non-zero angle with respect to said longitudinal axis andsloping toward said sixth sub-surface; and an eighth sub-surfacecontiguous with said seventh and sixth sub surfaces, said eighthsub-surface being oriented at an angle with respect to said longitudinalaxis; said method comprising: contacting said third sub-surface with afirst portion of said first arcuate projection of said coupling whilemaintaining a first gap between said first sub-surface and a secondportion of said first arcuate projection of said coupling; contactingsaid seventh sub-surface with a first portion of said second arcuateprojection of said coupling while maintaining a second gap between saidfifth sub-surface and a second portion of said second arcuate projectionof said coupling; and applying a tensile force between said first andsecond pipe elements, thereby causing: said first gap to close, saidsecond portion of said first arcuate projection of said coupling toengage said first sub-surface, said second gap to close, and said secondportion of said second arcuate projection of said coupling to engagesaid fifth sub-surface.
 7. The method according to claim 6, wherein saidtensile force causes wedging between said third sub-surface and saidfirst portion of said first arcuate projection of said coupling and saidseventh sub-surface and said first portion of said second arcuateprojection of said coupling.
 8. The method according to claim 6 furthercomprising: contacting said second sub-surface with a third portion ofsaid first arcuate projection of said coupling while maintaining saidfirst gap between said first sub-surface and said second portion of saidfirst arcuate projection of said coupling; and contacting said sixthsub-surface with a third portion of said second arcuate projection ofsaid coupling while maintaining said second gap between said fifthsub-surface and said second portion of said second arcuate projection ofsaid coupling.
 9. The method according to claim 8, wherein said tensileforce causes a third gap to form between said second sub-surface andsaid third portion of said first arcuate projection of said coupling,and a fourth gap to form between said sixth sub-surface and said thirdportion of said second arcuate projection of said coupling.
 10. Themethod according to claim 6, wherein said second sub-surface is orientedat an angle less than 90 degrees with respect to said longitudinal axisto bias said first arcuate projection of said coupling towards saidthird sub-surface and said first sub-surface when said tensile force isapplied, wherein said sixth sub-surface is oriented at an angle lessthan 90 degrees with respect to said longitudinal axis to bias saidsecond arcuate projection of said coupling towards said seventhsub-surface and said fifth sub-surface when said tensile force isapplied.
 11. A method of forming a groove in an outer surface proximateto a first end of a pipe element extending along a longitudinal axis,said groove comprising: a first sub-surface oriented at an angle withrespect to said longitudinal axis and facing away from said first end; asecond sub-surface oriented at an angle with respect to saidlongitudinal axis, said second sub-surface being in spaced relation awayfrom and facing toward said first sub-surface; a third sub-surfacecontiguous with said first sub-surface, said third sub-surface orientedat a non-zero angle with respect to said longitudinal axis and slopingtoward said second sub-surface; and a fourth sub-surface contiguous withsaid third and second sub surfaces, said fourth sub-surface beingoriented at an angle with respect to said longitudinal axis; said methodcomprising: using an inner roller contacting an inside surface of saidpipe element and an outer roller contacting said outer surface of saidpipe element to roll groove said groove in said pipe element.
 12. Themethod of claim 11, wherein said inner roller and said outer rollercomprise corresponding profiles configured to form said groove.
 13. Themethod of claim 11, wherein said method further comprises rotating saidinner roller about a first axis, thereby causing said pipe element torotate which causes said outer roller to rotate about a second axis. 14.The method of claim 13, wherein said pipe element and said outer rollereach rotate as a result of contact friction between said inner rollerand said pipe element and said pipe element and said outer roller. 15.The method of claim 11, wherein said method further comprises forcingsaid outer roller toward said inner roller.
 16. The method of claim 15,wherein said outer roller is forced toward said inner roller via ahydraulic ram.